VMS Help FORTRAN, Data, Types, Logical  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Logical values start on an arbitrary byte boundary and are stored
  in one, two, or four contiguous bytes.  The low-order bit (bit 0)
  determines the value.  If bit 0 is set, the value is .TRUE.; if bit
  0 is clear, the value is .FALSE.  The remaining bits are undefined.